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Adventures in charging: too long an extension cord flips circuit breaker?

Discussion in 'Model S: Battery & Charging' started by ecarfan, Sep 10, 2014.

  1. ecarfan

    ecarfan Well-Known Member

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    My wife and I like to visit Sorenson's Resort in Hope Valley just south of Lake Tahoe, California. This year was our first visit with the Model S. I had contacted the resort and confirmed they had a 240V NEMA 10-30 outlet I could use. It was located in their laundry room and they used it for their electric dryer. They said it was about 75 ft. from the parking lot. They also had NEMA 5-15 110V plugs close to the parking lot, so I knew I had an alternative power source, albeit a very slow one.

    Sorenson's is only 88 miles from the Folsom CA Supercharger, but almost 7,000 ft. higher. So it would be an easy trip in an S85 but I certainly wanted to have reliable charging during my 3-day stay there. We got there with 66 miles of range left after charging to 205 at Folsom. I had brought with me 50 amp 125/250V 6/3+8/1 AWG 14-50 extension cords in 15 foot and 50 foot lengths, plus a 10 foot long NEMA 14-50R to 1030P adaptor which I bought here NEMA 14-50R to 10-30P or 10-50P Adapter

    Along with the Tesla UMC I figured that was enough length to reach the plug in the laundry room.

    So after arriving at Sorenson's I uncoiled all my cords and had no trouble making the connection. I started charging and was pleased -- and somewhat surprised -- to see that I was getting 40A at 240V. I watched it for 10 minutes and the charge rate was steady, so I went to my room. 20 minutes later I went back to the car to check on the charging and found that charging had stopped. I went to the laundry room and found the breaker for that circuit had flipped. I reset it, decreased the amp setting in the car to 30 and tried to charge again. Nothing. Turned amps down to 20 and tried to charge after unplugging the UMC at the car and plugging in again. No charging. Plugged the dryer back into the circuit and the dryer worked. So the circuit was intact.

    Tried resetting the breaker again, unplugging cables and replugging, all connections were tight (and new of course) but was unable to get the car to charge. So I got out my 25 foot 110V extension cord, changed adaptors on the UMC and plugged into 110V. Car started charging at 12A, 4mph rate of charge. I charged it continuously for the next 60 hours or so got up to over 200 miles of range before doing some driving 2 day later, charged again overnight and left the resort three days after I arrived with lots of charge. Of course it was easy to get back to Folsom because it was mostly downhill. In fact I could have made it to the Vacaville SC.

    I am guessing that the multiple 240V extension cords and the 10 foot long NEMA 14-50R to 1030P adaptor created too much resistance for the resorts elderly electrical circuit to handle for more than a short time. Does that seem likely? Thanks.

    Here's a photo of the extension cords running into the laundry room.

    Sorensons-charging-2014.JPG
     
  2. bollar

    bollar Disgruntled Member

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    If it was a 10-30, the MOST it should have supported is 24 amps. Given it was an old circuit, and because of all of the extension cords, I would have tried something under 20.

    Good thing the breaker tripped -- that wiring on that circuit likely can't handle 40 amps continuous.

    I guess I should say that is is what you need to be careful of when using adapters. If the Tesla thinks it's plugged into a 14-50, it's going to try to pull 40 amps. If it's a 30 amp circuit, the car will get 40 amps until the breaker trips (hopefully), or the wiring melts (ugh).
     
  3. Cottonwood

    Cottonwood Roadster#433, Model S#S37

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    Yes, you are lucky!

    The UMC and car assume a 50 Amp breaker when using the 14-50 adapter. NEMA says that for normal circuit breakers, a continuous load should not draw more than 80% of the breaker rating to assure that the breaker will not trip. If you use other adapters, then you have to manually back the car down to 80% of the breaker rating. Normally, a 10-30 will be served by a 30 Amp breaker, and you can draw 24 Amps.

    There are important exceptions. I have charged from a 10-50 that was served by a 40 Amp breaker and I had to dial the charge current back to 32 Amps. Also, I once encountered a 14-30 that was served by a 20 Amp breaker and I had to dial the charge current back to 16 Amps.

    Be careful with adapters. Always set the charging current to 80% or less of the connector rating. If the circuit breaker pops, figure out why. Never set the charge current to more than 80% of the breaker rating, and sometimes on old breakers you may have to back down to 50-70% of breaker rating; old breakers get tired.
     
  4. linkster

    linkster Member

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    I see this silliness more and more on new construction along with 14-50's on 40A breaker with NM-B 8 ga. I guess the breaker only needs to protect the weakest link in the circuit and is mainly for the romex behind the wall. However, I think it's shameful that the NEC (didn't they also bring us whole house alum branch circuits in 60-70's without fully understanding the co-efficient of alum expansion and that when alum oxidizes=resistance=heat=fires?) is bowing down to home builder pressure so that they can save a few a bucks on smaller gauge wire. When in the wild, you must check, check, and re-check and I rarely attempt to pull even 80% max amps.
     
  5. ecarfan

    ecarfan Well-Known Member

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    #5 ecarfan, Sep 10, 2014
    Last edited: Sep 10, 2014
    Thanks cottonwood. It seems that what I should have done is set the car to 20A and then plug in. Probably would have worked. Live and learn...

    What I don't understand is why turning down the car to 20A after the breaker tripped and resetting the breaker didn't work but the dryer plugged into that circuit worked fine after my attempt at using it to charge.
     
  6. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    There is a misconception out there that breakers are precision devices and will trip at 30.01 or 30.1 amps. Most people don't know that a breaker is permitted by UL standards to operate at 135% of rated current for up to 2 hours before it must trip. Of course, that's worst-case performance and those "tired" breakers usually end up tripping much sooner after being in service for a while. That's why Cottonwood's safety reminders (and my cautions against using non-Tesla adapters) are so critical.

    - - - Updated - - -

    Where are you seeing these receptacles installed? The NEC hasn't changed its amperage standards in a long, long time - in fact, they've actually raised them by permitting 75 degC terminations and 90 degC conductors over the past few decades.

    If in-home, what you're probably seeing is the choice of the kitchen range receptacle. 210.21(B)(3) permits a 40A circuit to be supplied via a NEMA 14-50 receptacle. Conductors are sized to the breaker (per art 210). Circuit rating (and therefore breaker size required) depends upon the appliance to be used. There are some ranges that call for a maximum circuit rating of 40A. I probably see more older homes with 40A breakers and #8 than I see newer homes.

    Welders are also permitted to use smaller circuit ratings based on the size and duty cycle of the welder. It's common to find a NEMA 6-50 attached to #10 wire and a 30A breaker in home garages because of this.
     
  7. ecarfan

    ecarfan Well-Known Member

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    #7 ecarfan, Sep 10, 2014
    Last edited: Sep 10, 2014
    FlasherZ, can you explain why, in the scenario I described in my OP, that turning down the car to 20A after the breaker tripped and resetting the breaker didn't result in my car charging but the dryer plugged into that circuit worked fine after my attempt at using that circuit to charge? Thanks for your comments!
     
  8. Zextraterrestrial

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    did you unplug the car and then re-plug after flipping the breaker? if that didn't work then
    you might need to make the car forget that location, then re-plug in with the amperage preset at a lower current

    I have had breaker trips where just flipping the breaker wouldn't automatically start charging again even though there was power in the outlet. needed to unplug and replug also
     
  9. ecarfan

    ecarfan Well-Known Member

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    Zextraterrestrial, yes I did do what you described.

    Next time I am there I will tell the car to "forget" that location before I plug in. Thanks!
     
  10. swaltner

    swaltner Member

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    I suspect the breaker had overheated, which is why it kept tripping, even when you turned the current down to 20 amps. If you let it cool down for 30 minutes before resetting, it probably would have worked at the lower amperage.
     
  11. Cosmacelf

    Cosmacelf Active Member

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    Yes, the breaker was almost certainly still too hot, so it needed to cool down for a while.

    I'm a bit alarmed that you managed to buy all these adapters and extension cords, yet didn't manage to understand what it was you were doing.

    As others have pointed out, the most you should have been charging at is 24 amps on that dryer circuit. You are lucky that you didn't start a fire. You may have cause some unseen damage to the wiring as it is.

    Please educate yourself on receptacles, amperage ratings and the like if you use third party adapters and extension cords. This document may help: http://cosmacelf.net/Home Made Adapters.pdf
     
  12. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    Sure. An electric dryer or stove is an intermittent load -- the heating element brings the cavity (oven, dryer) up to temperature then kicks off, allowing the conductors and terminations/breakers to cool off. It then cycles back on and off. Contrast this with a continuous charging load, where the car simply draws 20+ amps constantly for many hours.

    - - - Updated - - -

    Typically, this shouldn't happen - a reduction in the current should cause the breaker temp to stabilize. That said, there could be external factors - loose screws/connection on the breaker, or a panel exposed to direct sunlight, etc...
     

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